This invention relates to a boot for an automobile, composed of two terminal annular parts and a barrel part intervening between the opposite terminal parts and formed of a flexible PVC material. Particularly this inventions aimed at a shift lever boot, for example, to be used in an automobile and therefore expected to, most of all, appeal to the eyes of the automobile driver and passengers.
For the sake of explanation the present invention will be described below with reference to a shift lever boot 7 comprising, as illustrated in FIG. 1, two terminal annular parts 1, 3, one small and the other large diameter, and a barrel part 5 intervening between the annular parts 1 and 3. This invention is not required to be limited to this particular construction. It does not discriminate the automobile boot on account of the presence or absence of an intervening corrugated barrel part.
Generally most of the shift lever boots currently in use are products obtained by injection molding flexible PVC material.
The polymer component used for the flexible PVC material is generally of a grade having an average polymerization degree (hereinafter referred to as "P" for short) of about 2,500.
The shift lever boot, after protracted use on an automobile, develops the possibility that the barrel part thereof will yield to layer separation (swelling) and sustain heavy surface irregularities such as to impair the appearance of boot. Particularly when the automobile is left standing under intense heat in the summer, the interior of the automobile is heated to a very high temperature and the trouble of phase separation is brought on very quickly.
Mainly from the standpoint of design (color harmony of the automobile interior), shift lever boots of the delustered type are filling a growing demand.
Since PVC is capable of faithfully transferring a pattern on the surface of a metal die, such shift lever boots of the delustered type have been produced by using metal dies having surfaces treated by honing (one kind of crimping treatment).
When the number of injection molding cycles increases to the order of 5,000 to 10,000, the PVC material for injection molding buries the honed surface (crimpled surface) of metal die. When the metal die is washed for the removal of adhering PVC material, the honed surface thereof may be scraped off. If the metal die is further used, the shift lever boots are liable to be produced with a partially or wholly lustered surface. Thus, the metal die of the foregoing description has a disadvantage that it is liable to produce shaped articles of poor appearance.
Particularly shift lever boots of the type using a corrugated intervening barrel part has a disadvantage that, while in use in a cold district, their corrugated intervening barrel parts are liable to sustain cracks.